Rotating labyrinth seals have a wide variety of uses and one such use is to effect sealing between plenums at different pressures in gas turbine engines. Such seals generally consist of two principal elements, i.e., a rotating seal and a static seal. The rotating seal, in cross section parallel to the axial length of the engine, frequently has rows of thin tooth-like projections extending radially from a relatively thicker base toward the static seal. The static seal or stator is normally comprised of a thin abradable configuration. These principal elements are generally situated circumferentially about the axial (lengthwise) dimension of the engine and are positioned with a small radial gap there between to permit assembly of the rotating and static components.
Referring to FIG. 1 of the drawings, there is shown a partial view of an exemplary high pressure turbine section which is a section of aircraft gas turbine engine which typically utilize rotating labyrinth seals 1. The high pressure turbine includes a plurality of radially extending stage-one blades suitably mounted in a stage-one turbine and a plurality of radially extending, stage-two blades suitably mounted in stage-two turbine disks. The disks are labeled 8 and the blades 10. Stage-one blade 10 and disk 8 lie upstream in relation to downstream stage-two blade 10 and disk 8. The flow of hot gases in the high pressure turbine is from upstream to downstream, i.e., from left to right in FIG. 1.
The rotating labyrinth seal 1 includes a rotating portion 3 (comprised of fins 2 and base 4) and a stator or static seal 6. Rotating portion 3 is suitably mounted between the stage-one turbine disk 8 and the stage-two turbine disk 8. Stationary static seal 6 is attached to stage-two nozzle 12. The stage-one nozzle (not shown) lies upstream from the stage-one blades.
The rotating portion 3 comprises base 4 and a plurality of seal teeth 2 radially extending from the outer peripheral surface of base 4. The outer circumference of the seal teeth 2 rotate within a small tolerance of the inner circumference of the stator 12, thereby effecting a sealing between stage-one plenum 7 and stage-two plenum 9. Base 4, as shown, has an annular configuration and a generally arcuate cross section, but other configurations are frequently encountered in gas turbine engines. Seal teeth 2 may be attached to the base 4, as by welding, or be integrally machined in to the base 4 and extend in ring-like fashion circumferentially about base 4 and axial centerline (not shown).
When the gas turbine engine is operated, the rotating portion 3 expands radially more than the stator 6 and rubs into the stator 6. The rotating seal teeth tips are made thin in order to thermally isolate them from the supporting base 4 or shell structure.
The thin tooth (fin) 2 is, however, susceptible to handling damage which can result in cracks in the tips of the teeth opposite the base 4. Conventional rotating seals (knife seals or labyrinth seals) on discs 8 and shafts 114 (see FIG. 2) have commonly exhibited cracking in service caused by rub damage. These cracks may propagate into the torque-carrying load path. As shown in FIG. 2, the seals 1 are in the load path, or integral into the structure which carries the torsional loads between the compressor and the turbines, or between stages. FIG. 2 shows the seal fins 2 integrated in the shaft 14 and the disks 8. The crack propagation from the fins 2 could cause the shaft to break, causing turbine over speed and potential turbine disc burst (a hazardous event). The cracks could also propagate into the body of an integral disc, potentially leading to disc burst (a hazardous event).
The propagation of cracks in seal fins may also result in increased economic cost, even absent catastrophic damage. Cost associated with fleet inspections and adjustment of seal clearances as well as the cost of expensive coatings to avoid rub damage, may be minimized by reducing or eliminating the risk of crack propagation.
While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the present disclosure is not intended to be limited to the particular forms disclosed. Rather, the present disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims.